The present invention relates to a direct heating cathode structure for miniature cathode ray tubes, and particularly to a direct heating cathode structure for cathode ray tubes which improves the welding precision of a support for a coiled heater.
FIGS. 1 and 2 show an ordinary direct heating cathode structure mounted to an electron capable of producing an electron flow which reduces picture output time with lower power consumption. The cathode structure comprises an insulator 10 having a passing hole 10a at its center, a pair of inverted-L- shaped supports 11 secured on insulator 10 at a certain distance apart, and a coiled heater 12 with both ends welded onto the top of supports 11. The heater is coated with an electron emitting material.
Since the conventional direct heating cathode structure for cathode ray tubes has flat-topped supports 11 with heater 12 coiled into a small diameter and welded thereon, it is difficult to precisely weld coiled heater 12 onto the center of the tops of supports 11. If coiled heater 12 is off-center when welded to the tops of supports 11 and then mounted to an electron gun, the relative positions of the heater and a corresponding electrode are incorrect, making the thermions emitted from the electron emitting material coated on the heater difficult to control normally by an electron gun electrode. This improper positioning of the heater results in a poor cut-off emission characteristic of the electrode of the electron gun making control of thermions further difficult.
To solve this problem, according to the conventional method, welding is performed with a microscope for greater precision. This requires a rigid manufacturing process. However, this precision welding method of the heater delays the manufacturing process, resulting in low productivity. Further, since the precision welding of the heater depends on the naked eyes and fatigues a worker, the desired result is not easily obtained.